Oldest Dinosaur 'Nursery' Discovered

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Tiny prints from baby dinosaurs dot the oldest dino nesting site
found to date, a 190-million-year-old nursery in South Africa,
researchers said.

The hatchery and the baby footprints uncovered there are
significant clues about the evolution of complex
family behaviors in early dinosaurs, providing the
oldest-known evidence that dinosaur hatchlings remained at nests
long enough to at least double in size.

The newly unearthed clutches of eggs, many with embryos inside,
belonged to the plant-eating dinosaur Massospondylus, a
prosauropod, or predecessor of the largest animals to ever walk
the Earth,
long-necked sauropods such as Brachiosaurus.

How to unearth a dinosaur egg

The international team of researchers conducted their excavation
in the Golden Gate Highlands National Park in South Africa. The
nesting ground, now largely covered in reddish-brown muddy
siltstone, predates
previously known nesting sites by 100 million years.

"The eggs, embryos and nests come from the rocks of a nearly
vertical road cut only 25 meters (82 feet) long," said researcher
Robert Reisz, a paleontologist at the University of Toronto at
Mississauga. "Even so, we found 10 nests, suggesting that there
are a lot more in the cliff, still covered by tons of rock. We
predict that many more nests will be eroded out in time as
natural weathering processes continue." [ Photos
of dinosaur nesting sites ]

The eggs and nests proved difficult to unearth because the
eggshells are extremely delicate at less than 100 microns in
thickness, or less than the width of a human hair, making it easy
to inadvertently destroy them. "We literally spent days and days
searching for the eggs and nests, spending most of our time on
our hands and knees, but once we were able to recognize what to
look for, we found four nests within 10 minutes," Reisz told
LiveScience.

The nests unearthed to date each held up to 34 round eggs in
tight clusters. The skeletal remains of the mothers suggest they
were about 20 feet (6 meters) long, while their eggs were only
about 2.3 to 2.7 inches (6 to 7 centimeters) wide. The mothers
carefully arranged these eggs, the researchers say, basing this
on the high level of organization of the nests and eggs.

Dinosaur day care

From the fine-grained nature of the sediments holding the eggs,
the researchers think the nests were built near a lake or a
slow-moving river. "The fact that the nests are relatively close
to water, and the soil was moist, suggests that there was lots of
vegetation," Reisz said. This likely made the area attractive to
these herbivores.

And the site seemed to be a popular one for dino day care, as the
nests were found in at least three distinct layers of rock within
the excavation, each indicating a different point in time. In
fact, the researchers suggest the dinosaur moms likely returned
repeatedly to the site. Also, the fact that multiple nests were
found within the same layers — and thus were laid at about the
same time — reveals the dinosaurs likely gathered in groups to
lay their eggs, the oldest evidence of such behavior in the
fossil record.

"Even though the fossil
record of dinosaurs is extensive, we actually have very
little fossil information about their reproductive biology,
particularly for early dinosaurs," said researcher David Evans,
associate curator of vertebrate palaeontology at the Royal
Ontario Museum in Canada. "This amazing series of
190-million-year-old nests gives us the first detailed look at
dinosaur reproduction early in their evolutionary history,
and documents the antiquity of nesting strategies that are only
known much later in the dinosaur record."

The researchers are now slowly uncovering
embryos within these eggs. They have embryos in several
different stages of development, "allowing us to do actual
comparisons between them," Reisz said. "The preservation is
exquisite."

The scientists detailed their findings online today (Jan. 23) in
the Proceedings of the National Academy of Sciences.

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